NATO straps win on durability, price, and versatility, while leather straps win on looks and comfort for dressier wear. Neither is objectively better, they're built for different situations, and a lot of watch owners end up wanting both for the same watch depending on the day.
Why a NATO strap makes sense for daily wear
A NATO strap is a single piece of woven nylon that threads under the spring bars, which means even if one spring bar fails, the watch stays on your wrist instead of falling off. That alone makes it a smart choice for anything active, from workouts to travel to just a rough week where you don't want to worry about your watch. NATOs are also cheap enough to own several, dry quickly if they get wet or sweaty, and swap out in seconds without tools.
The tradeoff is bulk. A NATO adds thickness under the case since the strap doubles back on itself, and it can feel warmer against the skin in summer than a breathable leather strap would.
Why leather still wins for a lot of watches
Leather straps look better with tailored clothing and give a watch a more finished, intentional appearance, especially on a dress watch or a vintage-style piece like a Seiko 5 on a simple leather band. They mold to your wrist over time and generally feel more premium against the skin than nylon does.
The downside is upkeep. Leather doesn't like water, sweat, or humidity, and a strap that gets soaked regularly will crack and wear out faster than a NATO ever would. If you're rough on your watch or active outdoors, leather is the wrong tool for the job. If you're dressing up or want a classic look for everyday wear in a dry climate, it's hard to beat.